Russia’s Monday decision to suspend a memorandum of cooperation with the US-led coalition in retaliation after a US jet shot down a Syrian Army plane has rattled some US allies, who fear escalating tensions between Russia and the coalition. In what it called a "precautionary measure," Australia became the first coalition member to suspend flights in Syria, claiming it's too dangerous for its planes to fly without the agreement, according to BBC.

“As a precautionary measure, Australian Defense Force (ADF) strike operations into Syria have temporarily ceased,” Australia’s Department of Defense said in a statement, adding its operations in Iraq would continue as part of the coalition.”

“ADF personnel are closely monitoring the air situation in Syria and a decision on the resumption of ADF air operations in Syria will be made in due course.”

“Australian Defense Force protection is regularly reviewed in response to a range of potential threats,” the Department of Defense said.

Australia has deployed about 780 military personnel as part of the US-led coalition fighting the Islamic State in Iraq and Syria

The BBC notes that Australia has a small but highly capable contingent of six F/A-18 strike aircraft; a tanker; and an E-7A Wedgetail early warning aircraft, all based at Al Minhad in the United Arab Emirates. Most of the Australian strikes have been in Iraq, though its aircraft do also operate over Syria. Australian commanders will reassess the situation in due course. The more fundamental question is what the Russian threat actually amounts to. Is it just rhetoric or does Moscow want to deny certain areas of Syrian airspace to US-led coalition aircraft?

The Russian Defense ministry called the attack “an act of aggression,” on the part of the US-led coalition. The US military neglected to use a communication line with Russia concerning this attack, despite the fact that Russian warplanes were also on a mission in Syrian airspace at the time, the Russian Defense Ministry alleged, conflicting with the Pentagon's explanation of events.

The bilateral memorandum of understanding was signed between the United States and Russia signed in October 2015 to ensure the safety of flights during combat missions over Syria. In retaliation for the US attack, the ministry warned that Russian missile defense would intercept any aircraft in the area of operations of the Russian Aerospace Forces in Syria.

"In areas where Russian aviation is conducting combat missions in the Syrian skies, any flying objects, including jets and unmanned aerial vehicles of the international coalition discovered west of the Euphrates River will be followed by Russian air and ground defenses as air targets," the Russian Defense Ministry announced, quoted by Sputnik.

Contrary to the earlier statement by the US, according to which it "contacted its Russian counterparts by telephone via an established "de-confliction line" to de-escalate the situation and stop the firing", Russia claims the US-led coalition command didn't use the deconfliction channel with Russia to avoid an incident during an operation in Raqqa:

"Russian Aerospace Forces' jets were conducting operations in Syrian airspace that time. However, the command of the coalition forces didn't use the existing channel between the air command of the Qatari airbase al Udeid and the [Russian] Hmeymim airbase to avoid incidents over Syria."

We now wait to see which other US allies – Germany, Denmark, the Netherlands, France, Jordan and the UK also are contributing men and arms to the task of "liberating" Syria – will announce that they're temporarily pulling out of the conflict until tensions once again de-escalate.